Prosthetic devices may be placed in vessels and ducts for a number of medical procedures. Typically, placement of the prosthetic devices into the vessels and ducts functions to maintain an open passage through the vessel or duct. For example, where a biliary or pancreatic duct becomes occluded, it is often desirable to facilitate drainage through the duct by the placement of a tubular prosthesis within the occluded area. In some procedures, stents have been used to maintain an open passage.
The passageways into which the stents are placed may change shape and move in response to bodily movement of the patient. Stents designed for placement in these passageways are flexible to accommodate movement of the passageway. Stents are commonly made of polymers or metals, typically a shape memory alloy, and may include flaps or barbs at each end of the stent which serve to prevent migration and retain the stent in place. Some stents may have various pre-formed retaining configurations, such as pigtails or spirals, to help maintain the stent in position. Stents have also been formed into various expandable configurations so that, when the stent has reached the occluded area, the stent is expanded to press outwardly against the ductal wall and to thereby maintain its position within the duct. Biliary and pancreatic stents may be delivered using a catheter that may include a pusher from behind the stent that pushes against the proximal end of the stent until the stent has reached its desired location.
During the placement procedure, retaining elements, such as flaps and pigtails have been known to have an abrasive effect on the surrounding ductal tissue as they pass into the duct and through the obstruction or stricture, thus causing or aggravating inflammation of the duct. These retaining elements have also been known to cause aggravation inside the duct to tissue adjacent the retaining elements while the stent is left in place, and particularly, when the stent is removed.
There is a need for an improved stent which can be atraumatically placed within an occluded biliary or pancreatic duct and remain in place without causing aggravation to the ductal tissue, and which further can be removed with little damage or additional irritation to the duct. There is also a need for a stent having retaining elements for engaging a sphincter to hold the stent in position within the duct without causing aggravation to the ductal tissue.